Pregnant, Obese Women at Increased Risk for Early Delivery

The more excess weight pregnant women carry, the greater their risk for preterm delivery, study shows.

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Healthy pregnancies last at least 37 weeks, giving babies the time they need to grow and develop before entering the world. When babies are born prematurely (before 37 weeks of pregnancy), risk of death and other health problems drastically increase. Nearly half a million babies are born prematurely each year in the United States, and in past years, smoking was the most preventable risk factor for preterm delivery and low birth weight. Obesity, however, has now surpassed smoking as our biggest worry when it comes to risk for preterm delivery. More Americans are obese than ever before and according to a recent study, the more excess weight pregnant women carry, the greater their risk for giving birth to a premature baby.

This study, which was recently published in the Journal of the American Medical Association, followed nearly 1.6 million deliveries in Sweden between 1992 and 2010. Researchers collected information on the body mass index (BMI) of mothers and on the length of pregnancy. Pregnancies lasting less than 37 weeks were considered preterm, and researchers ranked preterm deliveries into extreme (22-27 weeks), very (28-31 weeks) and moderate (32-36 weeks).

After adjusting for factors like age and smoking status, they found that women’s risk for having a preterm delivery increased with their BMI. Women who were considered obese with a BMI of 40 or greater were nearly three times more likely to have an extremely preterm delivery compared to normal-weight women. And overall, the greater a woman’s BMI, the greater her risk for early delivery.

These findings are especially concerning as obesity rates continue to increase in the United States. More than one-third of U.S. adults are obese, and we know that risk of preterm delivery increases with increased weight. We also know that the earlier the delivery, the greater the potential health risks to the baby. So it’s important that women, especially those who are pregnant or are trying to get pregnant, make healthy lifestyle changes to promote a healthier weight. The consequences of early delivery can be very serious—even fatal—and the more we can do to help prevent preterm deliveries, the healthier babies will be both now and in the future.

Questions for You to Consider

How do I know if I'm overweight or obese?

There are a few easy ways to evaluate weight. First, you can use your height and weight to calculate your body mass index (BMI). A BMI between 18.5 and 24.9 is healthy, a BMI between 25 and 29.9 is overweight, and a BMI of 30 or greater is obese. And because BMI is not always a perfect assessment of weight, it is important to measure your waist circumference. A waist circumference greater than 35 inches for a woman and 40 inches for a man is overweight.